Interstellar has that classic time travel paradox: 1. Cooper needed NASA's coordinates to start with in order to eventually end up inside the Tesseract. Without those coordinates he would not have made it to the tesseract. 2. To be able to give himself those coordinates(which would eventually lead him to the tesseract), Cooper had to be inside the Tesseract beforehand. Once we understand how Christopher Nolan used the concept of alternate realities in Interstellar to save humanity in one of those alternate realities, we will realize that the paradoxes get resolved in the 5th dimension. Here's the plot of the movie. It might help understand things better. So, we see that Cooper ended up inside the tesseract, a 5 dimensional space designed by "they". What we need to understand is that the 5th dimension allows us to see the parallel universes or the alternate realities. So, to us what seemed like Cooper looking a...